290
E
P
I2
J2
I
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Loading Formulas
Block Loading vs Angle of Deflection
Load on a block is a combination of the load on the line passing through 
the block, plus a block-loading factor, which is determined by the angle 
by which the block turns the sheet. For example, a footblock that turns a 
sheet 180 degrees will see a load equal to twice the load on the sheet. 
A deck organizer, which turns a halyard only 30 degrees, will see just 52 
percent of the load on the halyard. 
Boat Type
Most load formulas assume a medium displacement monohull, but you 
can easily correct for other boat types. Multihulls and boats with canting 
keels or water ballast have great form stability and speed and will often 
carry sails very high in the apparent wind speed, so calculations must 
be done with this wind speed in mind. ULDBs are typically tender and 
often change sails or reef quite early, so loading may be done at 
relatively low wind speeds. For example, a modern trimaran may carry 
its blade jib in 25 knots of wind at speeds over 15 knots for an apparent 
wind of nearly 40 knots, whereas a ULDB will probably remove its #1 
genoa at about 15 knots of apparent wind.
Rig Dimensions
The following abbreviations are often used to describe various measurements on a sailboat. Precise  
technical definitions exist for each abbreviation, but the following is a list of simple descriptions:
Genoa System Loading
Because wind speed is squared, it is the most important variable and 
can greatly influence loading. Wind speed (the apparent wind) should 
be calculated for the specific sail being analyzed. For example, the #1 
genoa on a 7 m (25') boat might only be carried in 15 knots of wind, 
while the #3 blade on a Maxi-boat could well be carried in 40 knots.
To calculate loading on a genoa lead car, multiply sheet load by the 
load factor of the sheet. Most #1 genoas will deflect about 45 degrees, 
while a #3 genoa may deflect 75 degrees or more.
Lead car adjuster tackle load is dependent on the angle of deflection 
of the sheet in the lead car, but is generally assumed to be 0.3 of lead 
car load when deflection is 45 degrees and .05 of lead car load when 
deflection is 60 degrees.
Mainsheet System Loading
The formula for mainsheet loading is not as widely accepted 
as that for genoa sheet loads and should only be used as a rough 
guide for offshore boats from 9 - 18 m (30 - 60').
Traveler car adjuster load is generally considered to be 0.2 times 
car load.
.2 x Car Load
.3 x Car Load
.5 x Car Load
Angle of
defl ection
Load
factor
Angle of
defl ection
Load
factor
Angle of
defl ection
Load
factor
30°
52%
90°
141%
150°
193%
45°
76%
105°
159%
160°
197%
60°
100%
120°
173%
180°
200%
75°
122%
135°
185%
GENOA SHEET LOAD
English
SL = SA x V
2 x 0.00431
Metric
SL = SA x V2 x 0.02104
SL
Sheet load in pounds
SL
Sheet load in kilograms
SA
Sail area in square feet
SA
Sail area in square meters
V
Wind speed in knots
V
Wind speed in knots
LOA
Length overall - overall tip-to-tip length of the boat
I2
Height of staysail halyard above deck
LWL
Length waterline - length of waterline of the boat
J
Base of the foretriangle measured from the front of the
mast to the intersection of the forestay and deck
DWL
Design waterline - theoretical waterline length of boat 
as opposed to LWL, which is actual waterline length
J2
Base of staysail triangle
BMX
Beam maximum - width of the boat at the widest point
P
Luff  length of the mainsail
BWL
Beam waterline - widest beam of boat at the waterline
E
Foot length of the mainsail
I
Height of the foretriangle measured from the top of the 
highest sheave to the sheerline
LP
Shortest distance from headstay to the clew of the jib
MAINSHEET LOAD
English
Metric
ML = E2 x P2 x 0.00431 x V2
(   P2 + E2) x (E - X)
ML = E2 x P2 x 0.02104 x V2 
        (   P
2 + E2) x (E - X)      
ML
Mainsheet load in pounds
ML
Mainsheet load in kilograms
E
Foot length of main in feet
E
Foot length of main in meters
P
Luff  length of main in feet
P
Luff  length of main in meters
V
Wind speed in knots
V
Wind speed in knots
X
Distance from aft end of boom to
mainsheet attachment point in feet
X
Distance from aft end of boom to
mainsheet attachment point in meters
Formulas are for typical cruising monohulls with fixed keel and Dacron sails, sheets, and 
halyards. Assumes standard roach of 7.5%. For large roach sails such as “flattops” multiply 
calculated load by the percentage of the mainsail roach. If a sail has 25% roach, multiply the 
calculated load by 1.25. For all other types, please contact Harken for technical assistance in 
calculating loads. 
Formulas are for typical cruising monohulls with fixed keel and Dacron
® sails, sheets, and 
halyards. For all other types, please contact Harken for technical 
assistance in calculating loads.
Dacron is a registered trademark of E. I. du Pont de Nemours and Company or its affiliates.

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